ELECTROCHEMICAL DESALINATION OF CORES FROM A REINFORCED-CONCRETE COASTAL STRUCTURE

This paper describes a laboratory investigation of the process of elec trochemical desalination (chloride removal) applied to cores taken fro m the splash zone of an eight-year-old reinforced concrete quay wall s ituated on the North Sea coast. The concrete, which had been made from blastfurnace slag cement in accordance with Rijkswaterstaat specifica tions, was of high quality and significant levels of chloride contamin ation were present only in the exposed surface zone of the material at depths well below the thickness of cover to the reinforcement. Segmen ts of steel reinforcement present within cores taken from the structur e were subjected to cathodic polarization at current densities in the range 0.6-4 A/m(2) for 3-6 weeks. The anodes, which were placed at the chloride-contaminated end surfaces of the cores, were composed of act ivated titanium meshes in contact with electrolyte solutions of either saturated calcium hydroxide or 1 M sodium carbonate. Changes in the e lectrical resistance of the concrete, its chloride content and its por e solution composition profile were measured and the corresponding inc reases in the chloride concentration of the external electrolyte were recorded. The proportion of chloride ions removed from the cores was f ound to depend on the total charge passed and on the nature of the ext ernal electrolyte, the efficiency of the desalination process being mu ch higher when saturated calcium hydroxide rather than I M sodium carb onate was used. The mechanism of this effect and the associated change s in pore solution chemistry are examined.